This invention relates to a metal hydride reactor.
It is known that many metals or alloys occlude hydrogen exothermically to form metal hydrides, and the metal hydrides reversibly release hydrogen gas endothermically.
LaNi.sub.5 H.sub.x, MmNi.sub.5 H.sub.x, MmCo.sub.5 H.sub.x, FeTiH.sub.x, VNbH.sub.x and Mg.sub.2 CuH are among examples of metal hydrides which are suitably used because of their ability to occlude a large amount of hydrogen and to release a large amount of the heat of reaction. In recent years, there have been proposed various metal hydrides devices such as heat pumps or hydrogen storage devices which utilize these properties of the metal hydrides.
A metal hydride reactor is known which comprises a large pressure vessel and a heat medium flowing pipe extending therethrough so as to perform heat exchange between a metal hydride in the vessel and the heat medium (Japanese Laid-Open Patent Publication Nos. 7057/1977 and 92144/1977). This type of reactor, however, must be large-sized because of the presence of the heat medium flowing pipe and its heat capacity is so high as to cause a decrease in heat efficiency. Furthermore, the apparatus is complex and large-scaled in order to withstand the volumetric expansion of the metal hydride incident to the occlusion of hydrogen. Moreover, since the area of is heat-conducting surface is small and the heat conduction and diffusion of hydrogen in the reactor are insufficient, the rate of the reaction is slow, and its output as a heat pump is low.
There is also known a reactor which is adapted to exchange heat through its outer wall instead of the heat medium flow pipe within the pressure reactor vessel (Japanese Laid-Open Patent No. 94192/1981). This type of reactor has the advantage that its heat capacity is smaller than that of the internal heat-exchanging type reactor. However, the diffusion of hydrogen is insufficient, and its resistance to the volumetric expansion of the metal hydride is low.
A reactor has also been suggested which comprises a pressure vessel and a hydrogen gas flow passage formed therein (Japanese Laid-Open Patent Publication No. 14210/1977). This reactor is improved in regard to the diffusion of hydrogen. But its resistance to the volumetric expansion of the metal hydride is still insufficient, and the conduction of heat from the metal hydride to a heat medium is low.
In a metal hydride device utilizing metal hydrides, the metal hydrides fill pressure vessels, and the hydrogen occluding and releasing reactions are carried out in the pressure vessels. During the repetition of hydrogen occlusion and releasing, the metal hydrides disintegrate into fine powders having a size of several microns. This reduces the conduction of heat between the metal hydrides, and the reaction does not proceed rapidly. Another problem is that when the finely divided metal hydrides densely gather at the bottoms of the pressure vessels, there is a risk that the pressure vessels will break when the volume of the metal hydrides expands incident to hydrogen occlusion, and hydrogen gas is not fully diffused to that part of the vessel in which the metal hydrides are densely packed.